The present invention relates to a microwave tube collector assembly and, more particularly, to a microwave tube collector assembly having a conductive thin film on the inner circumferential surface of a metal cylinder.
A microwave tube collector assembly recovers an electron beam emitted from an electron gun. In the collector assembly, a metal cylinder is called a collector core and is closed at one end to have a bottom for directly recovering the electron beam. When the microwave tube is operated, the electron beam collides against the inner circumferential portion of the collector core. At this time, secondary electrons are emitted from the collector core. The secondary electron emission largely depends on the metal material of the collector core. In general, the average number of secondary electrons generated per electron of an incident electron beam is called a secondary electron emission ratio.
As the material of a collector core, oxygen-free copper having a high thermal conductivity is mainly used in consideration of heat generated by collision of the electron beam. However, the secondary electron emission from the oxygen-free copper causes a relatively large decrease in overall microwave tube efficiency. In addition, the secondary electrons emitted from the collector core are returned to a slow wave circuit, and the microwave tube may fail to amplify. As shown in FIGS. 5A and 5B, therefore, a coating having a low secondary electron emission ratio is formed on the inner circumferential surface of a conventional collector core to suppress secondary electron emission. In FIGS. 5A and 5B a conventional microwave tube collector assembly is shown, reference numeral 15 denotes an oxygen-free copper collector core having an outer diameter of 40 mm, a length of 120 mm, and a cylindrical recess portion having an inner diameter of 30 mm and a length of 100 mm, and reference numeral 16 denotes a carbon thin film coated on the inner circumferential surface of the oxygen-free copper collector core 15 and used for suppressing secondary electron emission. Reference numeral 17 denotes a large number of heat-radiating fins extending on the outer peripheral surface of the collector core 15 along the axial direction of the collector core 15.
In the above conventional microwave tube collector assembly, secondary electron emission from the collector core 15 is suppressed by coating a thin film consisting of carbon or the like which has a secondary electron emission ratio lower than that of an employed collector material on the inner circumferential surface of the collector core. However, since the inner circumferential portion of the collector core 15 generally has a small diameter and a large length, it is difficult to easily and uniformly coat the thin film consisting of carbon or the like on the inner circumferential surface of the collector core 15, and the large number of steps are undesirably required in this operation. In addition, when this operation is performed, the thin film 16 consisting of carbon or the like has a low adhesion strength on the inner circumferential surface of the collector core 15. For this reason, a part of the film 16 is removed during an operation of the microwave tube, thereby considerably degrading the performance of the microwave tube.